With the emergence of new services such as Video On Demand (VOD), high definition television, and online games, the bandwidth required by users is increasing. The development of the Fiber-To-The-Home (FTTH) ensures the last mile bandwidth of the access network. The Passive Optical Network (PON) technology eliminates the active nodes in the traditional access network, and helps cut back maintenance expenses of the operators, and is one of the most popular FTTH technologies currently.
The existing PON standards include: the Broadband Passive Optical Network (BPON) and the Gigabit PON (GPON) developed by the Full Service Access Network (FSAN) organization and formulated by the ITU-T; and the Ethernet-PON (EPON) formulated by the IEEE organization. The coverage of the existing PON is 20 km, and the uplink rate and the downlink rate of the existing PON are of the gigabit magnitude. With the emergence of the next-generation optical access network, large operators such as British Telecom (BT) raises the requirement of extending the PON to be a 100 km distance. In January 2006, BT, Siemens, Alcatel, CIP and other companies and institutes initiated the Photonic Integrated Extended Metropolitan Area Access Network (PIEMAN) project in Europe, and raised the system objectives of a 10 Gbps symmetric rate, a 100 km transmission distance, and a 512 split ratio. The distance extension of the PON is conducive to integrating the access network with the Metropolitan Area Network (MAN), reducing network nodes required, and cutting back the maintenance expenses.
With the development of the PON, GPON-over-OTN architecture is currently applied, as shown in FIG. 1. This architecture implements distance extension of the GPON by increasing the access radius of the GPON through an Optical Transport Network (OTN). In this architecture, many Optical Network Units (ONUs) are connected to an optical splitter through fibers. The optical splitter is interconnected with the OTN device 1. An Optical Line Terminal (OLT) is interconnected with the OTN device 2 through fibers. The OTN device 1 is connected with the OTN device 2 through the OTN. When the GPON or the OTN fails, the GPON or the OTN performs protection switching separately. The protection switching based on the GPON-over-OTN architecture is described below:
GPON protection switching is generally described below.
When the GPON network raises an alarm related to signal loss, frame loss, or signal failure, protection switching is triggered between the active traffic channel and the standby traffic channel. The following four types of protection are available:
Protection type A: Only the backbone fiber is backed up. Neither ONU nor OLT is backed up.
Protection type B: The OLT is protected through cold backup, the optical splitter port at the OLT side is backed up, the backbone fiber is backed up, and the ONU is not backed up.
Protection type C: The OLT and all ONUs are protected through hot backup, the Optical Distribution Network (ODN) is backed up, which is known as full backup.
Protection type D: The OLT and some ONUs are protected through cold backup, and the ODN is backed up.
OTN Protection Switching
In 1998, the ITU-T puts forward the concept of OTN. The ONT transmits various client signals transparently, performs multiplexing, transmission, routing and amplification on the optical domain, and supports flexible network scheduling and networking protection. When the OTN network raises an alarm, the alarm triggers protection switching of the OTN. The OTN protection mechanisms recommended by the OTN network protection switching standard G.872 include: path protection mechanism, subnet connection protection mechanism, and shared protection ring mechanism.
In the process of developing the present invention, the inventor finds at least these defects in the prior art: When the OTN fails, for example, when a fiber is cut or the GPON Transmission Convergence (GTC) frame of the transmitted service is lost, the OTN raises an alarm to trigger the OTN protection switching. In this case, although the PON works normally, the PON is unable to receive the GTC frame normally, thus resulting in futile alarms and switching of the PON.